Fusible link constructions have been used for releasing a locking mechanism, closing of a fire door, releasing a sprinkler operating lever, and the like. Conventionally, such mechanisms have a weight or spring-biased actuator maintained in a non-operating position against the bias of the weight or spring by means of the fusible link which, in response to an increase to a predetermined level of the ambient temperature, separates and enables the bias imposed on the operator to move the latter from its non-operating position to its operating position.
Various kinds of fusible links have been proposed heretofore, one of the most common of which comprises a pair of flat plates arranged side-by-side and separably bonded to one another by a thermally sensitive substance which liquefies when its temperature is raised to a predetermined level, thereby destroying the bond between the plates and permitting them to separate.
One of the disadvantages of the side-by-side plates bonded to one another is that thermally sensitive bonding material has a tendency to creep over a period of time, particularly if it is subjected to tensile or compressive forces. In time, therefore, the bonding material may creep to an extent that it is incapable of maintaining the plates in joined condition or causes shortening or elongating of the assembly to the point that proper operation of the mechanism whose operation is to be controlled cannot be ensured.
One type of fusible link assembly designed to prevent creep over time is disclosed in U.S. Pat. No. 4,346,554 issued Aug. 31, 1982. In this construction two body members are separably coupled to one another and normally prevented from separating by a collapsible strut. One body member has an opening within which the other body member is slideably accommodated. The strut is accommodated within the opening and reacts between the two body members to preclude movement of the slideable body. The strut includes a eutectic alloy which liquefies when its temperature rises to a predetermined level which, in turn, permits the overall length of the strut to shorten, thereby enabling the abutment of the slideable body to pass through the opening in the other body and effect separation of the bodies.
U.S. Pat. No. 4,532,681 issued Aug. 6, 1985, discloses a fusible link wherein a first member includes a cylindrical aperture of a first diameter and a second member includes a cylinder of a second diameter less than the first diameter. The second member is received within the cylindrical aperture. Thermally sensitive solder joins the two members. A spring biases the first member away from the second member so that, when the temperature increases above a predetermined level, the solder liquefies and the two members are separated by the spring.
Other types of fusible links include flat members arranged side-by-side and having a dimple and projection arrangement, or a tongue and groove arrangement to prevent creep.